Since
we're heading to lower sunspotnumbers it was time to consider an antennaproject
for the lower HF-bands. We all tend to start with a dipole which we
usually can hangup in a decent way from 20 to maybe 30 meters. For
40 and 80 meters the dipole will have a length which becomes difficult
to hang up fully horizontal . This is usually the length where some
HAMS may come to the very painfull constatation that the lot or available
space to play with antenna's should be much bigger (for an antenna
freak, the lot should ALWAYS be bigger). Of course we can hangup the
antenna in inverted vee, of course we can bend the ends, of course
we can use techniques to shorten the dipole. This article and related
physicall testing is ment to try to find an alternative for the horizontal
dipole. Antenna efficiency, antenna pattern, used space and user satisfaction
are taken into account.

STARTING
POINT.

We will take an
inverted V for 40 meters, an antenna which is widely known amoung
HAM's as an allround antenna . Many know what to expect from a dipole,
I will try to compare this allrounder theoretical and practical with
a shorted VERTICAL dipole antenna which can be set from 10-40 meter.

Standing
in the garden on 4 m². Antenne is placed 140 Cm above ground on an isolating
tube.

DECISION
MAKERS.

A well known item by DX-ers are elevation
patterns. Due to many discussions about take-off angles, we might assume
to easily that we need as much energy at as low as possible angles
to work the DX. I believe you need the energy at the right angle at
the
right
time and I don't expect an antenna which radiates straight up to
be my main DX tool.

In
FIG.1 we see several elevation patterns from wel known antenna's. Pink
marked we see the elevation pattern from the inverted-V, which I
modelled at a moderate hight of 1/4 Lambda.
With this antenna we can see that a lot of the energy is goes upwards
to the sky. This will make the
antenna a champ for local contacts within the 800 km range. Even
at this moderate height, this inverted VEE will need a 10 meter high
support and a 20 meter long garden strip!

The
black pattern gives the radiation from a short vertical dipole with
capacitive HATS and coils for some center loading and exact tuning.
At a 24° angle you can see that it gives as much energy as the
inverted-V dipole. At lower angles there is little more and at the
higher angles you will be below the dipole. Very interesting is to
see how
the place of the antenna is affecting the pattern, for worst case
I assumed AVERAGE ground conductivity of 15 mS/m.

The
blue pattern gives you an idea about performance if you can place
this antenna in rich soil. I already started to glance after calculating
those patterns.

And...
if you're near salt water or go to an island expedition, there is
absolutely no reason to do much effort in putting up horizontal antenna's,
unless you can hang it as high as a wavelength.

The
modelled inverted-V antenna is full size and will have a higher
efficiency than a shortened horizontal dipole. If we consider
a full size 1/4 wavelength vertical we need
a 10 meter high radiator and enough radials for low angle radiaton
and appropriate efficieny. I will not go into the theory on the amount
of radials needed but even if you only use 4 of them you need a big
square to install the vertical antenna for 40 meter
(we
didn't consider 80 meter yet !!). Some HAM's may
not see the problem, but in a small country like Belgium a small lot
of 800 square
meter
will be "average" for many HAMS, and of course our XYL
don't want us to spoil the whole garden with wires hanging "around".
Placing the dipole not horizontal but vertical with cancel the energy
which
goes
upwards
and provide
low angle radiation depending on the conductivity-properties of the
ground in the environment (several wavelengths around your antenna).
If you're not in the desert you might have some advantages in using
the dipole vertical. A full size vertical dipole for 40 meter will
also be about 20 meter high, which might also be difficult to manage.
Shortening the antenna will able us to accomodate the antenna. The
most efficient way to load an antenna is top loading,
if we load the antenna with coils we will have to
deal with losses in the coil which can very fast turn into "heat
radiators" intstead
of radiators for our valuable RF-power. Instead of using the full
size vertikal dipole or inductively loaded shorter dipole or monopole
we
can reduce the antenna size without loosing much gain by using capacitive
HATS or a combination of both for lower bands. Hats are symmetrical
arrays of wire at right angles to the dipole ends.It is the
symmetry which results in radiation cancelling and hence does not
yield significant horizontally
polarized radiation. Non symmetry will not have much influence on the
radiation, but will reduce the operation bandwith with a significant
amount. The vertical dipole which we will test can be used with capacitive
toploading from 10 to 20 meters, if you add some high-Q coils at
the feedpoint you can use it on 30 and 40 meters too....BY SHORTEN
THE ANTENNA THIS AMOUNT, WE WILL MAINLY LOOSE BANDWITH RATHER THAN
GAIN.

BANDWITH
CONSIDERATIONS.

The bandwith of an antenna is one of the important issues
when we evaluate an antenna. I always assume operating bandwith to be 1.5:1
VSWR bandwith, higher VSWR values will require automatic or manual
impedance matching.

On 10 and 15 meter there is only a small amount of shorting,
so operating bandwith is wide enough to cover those larger bands.

On 20 meter we can easily cover 350 KHz with the shorting
HATS.

30 and 40 meter do need the coils placed
at the feedpoint, bandwith decreases to about 100 KHz due to the coils,
but this isn't a problem on those bands. The Q-faktor increases and
also the receive performance.

6
uH coils, 11Turns on 50 mm with 4mm² Cu wire. By increasing the
winding spacing will increases the resonance frequency. Coil in the serves
as B-match.

FROM 10 TO 40 METER.

Before we start with some construction details, lets look
into the calculated patterns and SWR curves.

On
10 meter the vertical is almost full size and provides a 17 degrees
take-off angle, current distribution
is also shown in pink over the EZNEC 3.0 Model. Impedance transformation
75/50 ohm may be considered.

15
meter is quite similar to 10, Hats are extended with tapered elements,
hose clamps allow tuning of the hats for your own prefered mode, CW or SSB.

Another
tapered section to prolonge the hats. Tuned to 20 meter provides you with
a nice small 20 meter vertical which can be used on a very small place,
no need for radials but good ground conditions will bring this antenna
to "live". (Pattern for average ground)

From
30 meter we have to insert the air-coils and add a B-matching coil to bring
the impedance to 50 ohm.

The
final 40 meter vertical dipole, shorted to a handy antenna which you can
build easily yourself, suitable to travel and place on holliday locations
or just in your QTH garden.

GAIN.

If we compare the patterns to, for example
a shorted HORIZONTAL dipole we will be lower in gain but the pattern is
omnidirectional and the
energy is used where we might need it. Blue is the shorted Horizontal
dipole, the black trace is the vertical dipole. <more patterns>

CONSTRUCTION DETAILS.

Below I propose a building schematic,
some room is left for individual tuning to own preferences or to improve
mechanical
strenght.
The antenna described is a testmodel and the prototype has been installed
since last summer at the QTH of my antenna fellow Franki, ON5ZO, who has
done some contest and DX testing after an initial testdrive by
the author.

MORE CONSTRUCTION
PICS...

One
of the coils for tuning the antenna on 30Meter or 40 Meter. 11 turns
of 4mm²
isolated Cu wire will allow you to tune to 7 Mc. When you open the coil,
you can bring the resonance to 10.125 Mc.

When
adding coils, the impedance drops to about 20 Ohm. A Beta matching circuit
is used
for impedance-transformaion to 50 Ohm. A balun or coiled feedline will
be needed to cancel return currents.

The
assembled vertical dipole here shown in th 10 meter version.

With a
M5 bold the drilled HAT sections are secured.

Upper and lower HAT
basic sections.

Balance
checking, none of the ends touches ground !

Tapering for tuning
and band change.

Half the
hat with tapered sections.

A completed hat for
876 grams.

B-MATCHING THE
SHORT ANTENNA.

When shortening an antenna this amount, the GAIN
will be lower, the bandwith smaller (higher Q),and feedpointimpedance lower.
The unmatched feedpointimpedance is 14,91-J26,3 Ohms. The amount of reactance
(-j26,3) will serve as capacity in our Beta matching network.

XL
= 32,59 WHICH CORRESPONDS TO A 0,73 uH COIL ON 7,025 MHz. COIL CAN BE
SEEN IN ABOVE CONSTRUCTION
PICTURES.

ON THE AIR.

After placing the antenna at my own QTH,
near Gent, I asked my good friend ON5ZO, Franki, to do some real testing.
As a dedicated DX-er
and contester, ON5ZO used the antenna at his brand new QTH from march
2003.

In July 2003 I asked him about 40 Meter...

A61AR United Arab Emirates
VK2KM Australia
TA3/G3AB Turkey
UN4L Kazakhstan
TO5AA Martinique
D4B Cape Verde
3V8BB Tunisia
TA3DD Turkey
A61AJ United Arab Emirates
SU9NC Egypt
9K9X Kuwait
JY9QJ Jordan
UN7IKD Kazakhstan
W5AA/HP3 Panama
W2LNB United States
K3WU United States
PR7AR Brazil
VU3KJB India
JY9NX Jordan
UN7TS Kazakhstan
A61AR United Arab Emirates
UN2E Kazakhstan
4J6ZZ Azerbaijan
E21CJN Thailand
EX2M Kyrgyzstan
TK5EF Corsica
YB0DPO Indonesia
4K0CW Azerbaijan
9H3TM Malta
A61AR United Arab Emirates
JY9QJ Jordan
K5MA United States
KC1XX United States
N3AD United States
WA3AAN United States
WJ9B United States
K9MUG United States
KC1F United States
W1EBI United States
K2NG United States
AA3B United States
N3RD United States
UN9LW Kazakhstan
KB1EFS United States
N2NT United States
KT3Y United States
N2ED United States
PY2NY Brazil
K7SV United States
N9RV United States
K3CR United States
AY0F Argentina
UN7CZ Kazakhstan
K3DI United States
XM3AT Canada
WW2Y United States
VA3DX Canada
K1NA United States
N4CW/1 United States
W1FJ United States
K1PT United States
KD4D United States
K8GL United States
K4JA United States
W8KIC United States
W8LU United States
TA2ZF Turkey
VE3NE Canada
K1TTT United States
VY2ZM Canada
JA3YBK Japan
JA6OLZ Japan
4K0CW Azerbaijan
4Z5LY Israel
N4AF United States
W2AX United States
K3KO United States
4J6ZZ Azerbaijan
KQ3F United States
K3GHH United States
VE3KZ Canada
KE9I United States
VE9DX Canada
K5KG United States
K1UM United States
VE3DZ Canada
TA3DD Turkey
H2G Cyprus
VE3WO Canada
VE1ACU Canada
K9BGL United States
TI3M Costa Rica
W3RJ United States
K5ZD United States
K3EST United States
VE3RM Canada
KD2RD United States
N2GC United States
ZL6QH New Zealand
KU1CW/0 United States
W4PM United States
LU4FM Argentina
E21CJN Thailand
EX2A Kyrgyzstan
A45WD Oman
4L8A Georgia
HS0ZDZ Thailand
K2PS United States
K2UOP United State
...

ON5ZO Comment :

First of all, I want to thank Kurt
ON4BAI for letting me use and test the prototype of his 40m vertical
dipole. I just moved to this QTH, and even up to now
there is a lot of work to be done, so there is not much time to install
antennas. Kurt's offer was gladly accepted: no more worries about 40m.

Some statistics? I've been using
the antenna for about 8 months now, during which I made about 1100 CW
QSOs on 40m alone, yielding a total of 97 DXCCs on 40m.
All with this antenna, from my QTH, with 100W.

How does it play? Well, I am very
satisfied with this antenna. Previously (at another QTH) I used a delta
loop and a quarter wave vertical with 50 radials on
40m. All of these have their benefits and drawbacks. The vertical was very
noisy to listen to, and lawnmowers don't really like the radials in the
lawn. But it was a good DX antenna. The delta loop was very good too,
especially for DX. Much quieter than the quarter wave and it doesn't
need radials. But you need a support that's high enough to support the
apex. I also had the impression that the loop slightly favoured a direction,
and was not really 'omnidirectional'.

Now, this vertical dipole combines
the benefits of these two into one antenna. It is reasonably quiet to
listen to, there are no radials, and I seem to work
all CW DX I hear on 40m. It plays good in EU too, which is nice for contesting.
So far, I have been working all that I could hear. NA, SA, AF, OC, JA's
- all worked on a regular base. In SSB, I work EU in some local contests
and always get good comments on the signal. I can even work K4JA on phone
and have heard VK/ZL on phone - but don't bother to call those.

Mechanically, I have a bit of a
weak prototype. The base is guyed in 4 directions, but the antenna is
very flexible. We have had severe winds and strong gusts,
and the antenna swings around, but never once did it bend, fall or fail.
For a permanent version, slightly bigger tubing won't hurt, but this
prototype survived so far.

Apart from it's electrical qualities,
I think this antenna has some other benefits as well. It's easy to construct
and assemble, does not require high towers
or poles, not much guying, low profile.

Imagine 4 of these in a 4 square array.

Franki ON5ZO

SWR-measurements.

I tuned the antenna at my QTH for 40
meter CW. EZNEC 3.0 is accurate, but building the coils implements some
tolerance. Therefore
I tuned the antenna with the AEA-CIA HF ANALYZER. Although I could easily
tune the antenna at my QTH, We found the antenna off-frequency after
transport to the ON5ZO QTH. To be honest, we didn't do much effort to
solve this trade off and Franki used the antenna with the autotuner from
the TS-850SAT tranceiver.

CONCLUSIONS.

This project will provide you with
a good antenna to work DX on 40 meter on a very limited footprint
and even with limited mechanical skills you can build one yourself
for an attractive budged.

We, ON5ZO and myself found a little frequency
shift in function of the weather. This is a minus in which we will
investigate to make it more stable.

It is a nice small antenna to put in the garden and
if your partner or neighbour can't stand this type af antenna, your
defenitely in the wrong HAM-environment.

The satisfaction is all yours if you work the ultimate
DX with your homebrewed antenna-"construction".